Air-cooled engine



Jan. 1, 1929. 1,697,818

'c. F. KETTERING AIR cooLsn ENGINE Filed April 17, 1922 5 Sheets-Sheet 1 Jan. 1, 1929. 1,697,818 c. F. KETTERING AIR COOLED ENGINE w/1 File April 17, 1922 5 s s 2 Jan. 1, 1929.

C. F. KETTERING AIR COOLED ENGINE 5 sheets sheet Filed April 17, 1922 Jan. 1, 1929.

C. F. KETTERING AIR COOLED ENGINE Filed April 1'7, 1922 5 Sheets-Sheet Patented Jan. 1, 1929.

UNITED STATES PATENT OFFICE.

CHARLES F. KETTERING, OF DAYTON, OHIO, AS SIGNOR T GENERAL MOTORS RE- SEARCH CORPORATION, OF DAYTON, OHIO, A CORPORATION OF DELAWARE;

AIR-COOLED ENGINE.

. 1 Application filed April 17, 1922. Serial No. asst.

This invention relates primarily to improvements in direct air cooling systems for internal combustion engines.

This invention is a division in part of my copending application Serial No. 514.014,

filed November 9, 1921.

One of the main objects of the present invention is to provide a direct air-cooling system for internal-combustion engines especially suitable for automobiles in order that such engines when employed upon automobiles will ive a relatively high fuel economy, and mayv e operated at relatively high compressions without the objectional fuel knock which has heretofore operated to prevent the general commercial adopt-ion of air-cooled engines.

In carrying out the aims of the present invention there is provided an engine, the cylinders of which have attached thereto a number of radiating fins of a metal of high conductivity, the attachment of said fins to the cylinders being such that the heat generated in the englne cylinders can readily flow into the fins, thefaces of which are preferably located in the path of a stream of cooling air which may be provided'by means of a suitable fan. In the preferred embodiment of the present invention hereinafter described, the cylinders are constructed in accordance with the inventions contained in the copending application referred to. In carrying out the invention there is provided an internal combustion engine of the air cooled type operatingat compression. pressures in the cylinder which are higher than those generally utilized 1n commercial air cooled engines, and are as high and even higher than the compression pressures which are obtained in water cooled engines of the type generally utilized today in commercial automobiles.

A further object of the invention is to pro.- vide an internal combustion engine having a cylinder with high conductivity fins bonded thereto, the dimensions of these fins being predetermined, to secure a sufiicient efficiency of operation of the engine, and if desired to permit the engine to operate at maximum efficiency with an employment of the m1n1 mum amount of copper.

A further object of the invention is to provide an air cooled internal combustion engine having a high compression in which the number and dimensions of the high conductivity fins and the volume of air which flows over said fins is predetermined to permit the engine to operate at substantially full load Without knocking.

A still further obj ect'of the invention is to proylde an air cooled internal combustion engine 1n which the enginezoperates at high compression pressures without knocking and in which the .relation of the ;fin dimensions to the a1r propelling means is so predetermined that the air propelling meansabsorbs only a relatively small horse power from the engine for its operation.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present inven tion is clearly shown.

-F1g. 1 is a plan view partly in section of an engine embodying the present invention fragment of which is shown;

Fig. 2 is a side elevation partly in section Fig. 9 is a cross sectional view taken.

through the line 9--9 of Fig. 8; and

Fig. 10 is an enlarged view of a' diagrammatic and exaggerated nature showing in cross sectionthe bond between the fins and the cylinder wall.

Referring to Figs. 1 to 6 of the drawings the engine 200 which embodies the present invention is more completely described and illustrated in the copending application of Charles F. Kettering and Charles R. Short, Serial No. 553,938, filed April 17 1922, Which has matured into Patent No. 1,644,731 of Oct. 11, 1927. In order to understand the present invention the following brief scription of this invention is given:

The engine 200 includes a crank case 203 having its bottom closed by oil pan members shown mounted in an automobile frame, a

700 and 701, and. a plurality o1 cylinders 220, 221 supported by the crankcase 203.

In the engine shown there are 6 cylinders arranged in pairs each pair consisting of cylinders 220, 221. One of the cylinders 221 is shown in detail in Figs-4, 5 and 6. Cylinder 221 includes a horizontal base portion 222, a relativel thin vertical shell portion 223, and, the t icker head portion 224. The base portion 222 is formed with openings 225 for receiving a part of the valve mechanisms, and with holes 227 throu h which bolts may pass forsecuring the cylinders to the crank case. The groove 231 shown in Fig. 6 receives packing material in order to secure a tight joint between the cylinder base and the crank case.

The cylinder shell 223 has a vertical outer surface to which are attached a plurality of fin loops 237 which are briefly constructed of a continuous strip of thin relatively pure copper or other material of high heat conductivity. The method and apparatus for constructing these fin loops are described and claimed in the copending application of Charles L. Lee, Serial No. 478,793, filed June 20, 1921, now Patent No. 1,507,318 of made.

Sept. 2, 1924, and the manner of attaching the fins to a cylinder is described an claimed in my copending application Serial- No. 514,014, to which reference has been These fins are not all of equal height as shown in Figs. 4, 5, 6, those on the left-hand side of the cylinderbeing shorter than those surrounding the portions of the cylinder shell and the fins in the right-hand side of the cylinders, being shortened slightly. This arrangement. of the finning permits a closegrouping of all of the cylinders and facilitates the placing of the cylinders in pairs as shown in Figs. 1 and 2 with an intake pipe for a pair of cylinders. This arrangement of finned c linders is more particularly described and claimed in my copending application Serial No. 417,095, filed Oct. 15, 1920, now Patent No. 1,489,324 of April 8, 1924. The lower ends of the fin loops are provided with vertical slots 238 to permit cleaning dust and other foreign material from the inside of the loops by means of a narrow brush whose bristles project throu h the slots.

Each cylinder hea 224 is provided with intake and exhaust ports 239 and 240, respectively, and with a: hole 245 tapped to receive a spark plug 246, and with tapped holes 247 to receive bolts or the like for securing a superstructure 250 to a pair of cylinders The cylinder superstructure designated as a whole by numeral 250 is secured to the heads of each pair of cylinders 220 and 221, and includes a common intake 253 for a pair of cylinders, said intake having branches 254 and 255, communicating with the intake ports of cylinders 220 and 221, respectively. 256 and 257 are exhaust conduits leading respectively from the exhaust ports of the cylinders 220 and 221. Each superstructure 250 supports intake and exhaust valves which are actuated by rocker ture 250. These roc 'er arms 275 and 274 are actuated by push rods 288v which are moved upwardly by a timing mechanism not shown. Springs 264 normally retain engine valves upon their seats.

Fan belt driving pulley 808 is operated by the engine and drives through fan belt 810'; a'fan pulley 835 which drives fan 820 mounted upon a shaft 812 one end of which is supported by bracket 811 attached to the engine crank case, and the other end of which is carried by the fan spider 813 which in turn is supported by the engine superstructure 250 as shown in Fig. 2. The belt 810 is of the type as will give high efiiciency .withoutv being drawn taut on the pulley wheels as in prior practice thus reducing the pressure and power required to drive the fan. The power required for driving the fan is also reduced by. employing a fan of the peripheral discharge type having a large intake and discharge throat which w1ll give the fan a large capacity, the air being drawn out readily at a relatively low velocity. The fan 820, includes a fan outer wall 838 having an inwardly projecting center conoidal portion for deflecting the air entering the fan up toward the blades 839 which are supported between the fan outer wall 838 and the fan inner wall 840. This inner wall 840 has a rearwardly extending annular flange 841 which extends within the flange 814 of the fan spider 813.

A plurality of spider arms 816 serveto connoct the flange 814 with a fan shaft 812 and with a mounting pad 817 which is bolted directly to'the superstructure 250. The rotatlonvof the fan is clockwise as viewed in Fig. 3, and the blades 842 are so arranged as to push the air out of the fan with such pressure as to overcome the atmospheric pressure surrounding the fan but at the same time Without imparting to the fan exhaust a velocity which has a substantial effect on the efiiciency of the cooling system. The draft tube shown in Figs. 1 and 2 is designated as a whole by numeral 850 and comprises three principal sections 851, 852

and 853. Sections 851 and 852 have bottom draft tube portion 862 which cooperates with a movable tapered draft tube portion 853 to provide a housing for the superstructure and :valve mechanism and to provide a tube for conducting the cooling air to the circulating fan. Cover 853 is hinged at 863 so that the cover may be swung to one side to give access to the tube portion of the engine. When in position the cover 853 is secured by means of bolt members 864. These draft tube portions extend toward the front end of the engine to the fan spider 813. The draft tube 850 is attached to the en 'ine superstructure 250- by means of the T bolt members 889 and the clamps 892 which likewise secure the manifolds 870 and 871 to the superstructures, it being understood the dowel sleeves which connect the branches of the manifolds 870 and 871 with the various conducts 253, 256 and 257, pass through apertures in the vertical wall 856. v

The engine crank case 203 is provided with arms 206 and 207 by means of which the engine is supported upon brackets 208 and 209 forming the part of the automobile frame. frame members 213 and 214 respectively, which are connected at their free ends with a cross member 212 which assists in supportin the front end of the engine.

I will now proceed to describe the construction of the fins and their attachment to the cylinder walls. Referring more particularly to Fig. 7 it will be seen that the fins are formed from a strip of copper bent or crimped to the shape of the fins and in the embodiment here illustrated I have shown all the fins made from a continuous thin strip of copper. These fins are attached to the cylinder simultaneously and have their uniform treatment; that is, each fin is subjected to substantially the same condition as all the'other fins in the process of attaching the fins to thecylinder. The preferred process of attaching said fins to the cylinder is fully described in my copending application, Serial No. 514,014, filed November 9, 1921, and I shall not refer in detail to said process of manufacture herein other than to state that it involves the brazing of the fins to the cylinder walls by means of brazing metal such as brass or silver solder, and in the preferred form of said process for attaching the fins to the engine cylinder, a band of brazing brass 34, Fig. 7, is interposed between the faces of the fins and the cylinder wall 30. An iron wire 35 is tied around the assembly of fins and cylinder, and the assembly is placed in a suitable furnace. Owing to the difference in the coefficient of expansion of the copper fins and the iron of the iron wire 35, the fins are pressed against the bonding metal 34 during the heating operation, and an intermingling, alloying, union or penetration of the metal takes place during the These brackets 208 and 209 support It will be noticed with reference to the drawings that in Figs. 1 to 6 the fins are of unequal height while in Figs. 8 and 9 is illustrated a construction in which the fins are of uniform height. For purposes of convenience I term the finning illustrated in Figs. 1 to 6-eccentric 'finning, and the finning illustrated in Figs. 8 and 9-concentric finning. The purpose of the eccentric finning is to permit of bringing the en gine cylinders more closely together as more particularly described in my copending application, Serial No. 417,095, above mentioned. I

Referring to Figs. 1 to 6 it will be noted that the finning structure when assembled on the cylinder presents a configuration which is substantially eccentric with respect to the periphery of the'shell notwithstanding the fact that the faces of the fins are concentric with and attached to the shell. The finning structure consists of a plurality of fin loops 32, each loop including two fin portions exposed on both surfaces to cooling air and of base portions 33 connecting the lower loops 32. The distance from the base of the fin to the outer end of the fin is hereinafter referred to as the height H of the fin; the distance from the top edge of the fin to the bottom edge of the fin in a longitudinal direction is referred to as the length L of the fin; the distance between the center line of each fin loop and the center line of the adjacent fin loop is called the pitch P of the fin (see Fig. 7). It will be noted with ref erence to Fig. 7 that the faces of successive fins are contiguous to each other, thus forming approximately a circle and as a result of the process of manufacure of said fins as described in my said copending application, Serial No. 514,014, these base portions fol.- low the eriphery of the cylinder and preferably orm an encasing skin of metal around the entire outer periphery of the cylinder shell. thus forming extremely efficient heat conducting bond for attaching the fins to the cylinder. The nature of this bond will be understood more particularly with reference to Fig. 10 in which 145 represents a cast iron cylinder and 146 represents the zone of intermixture alloying or adhesion between the iron and the brazing solder, 147 represents the zone of solder, 148 represents the zone of intermingling, alloying or adas I am able to ascertain I believe that these zones are present in the completed structure. But the dimensions and thicknesses are exaggerated for the sake-of clearness, and are not intended to be accurately proportional. Microphotographs of sections of bonds produced by the hereindescribed process seem to indicate that there is a progressive merging metallic path for the conduction of heat from the iron to the copper, and tests tend to show that true thermal connection exists between the fins and theiron. At least this union ofi'ers considerably less resistance to the passage of heat than would be the case in a junction where the copper fins are merely in contact with the iron.

It will be noted from examination of Fig. 10 that the brazing solder has flowed up between the edges of adjacent fins during the brazing operation as indicated at 150, bonding these fins together, thus strengthening the roots of adjacent fins. The bases of adjacent fins are thus each interconnected by the brazing solder alloyed therewith so that there is formed a continuous skin of heat conducting metal around the outside of the cylinder from which the roots of the fins project and merge into the fins proper, the roots of these fins being preferably of greater thickness that double the thickness of the fins beyond the roots.

WVhile'it is desirable to have a continuous skin on the outside of the cylinder, as described above, as it permits of equalizing the distribution of heat in the outer surface of the cylinder, the invention is not limited to a bond between the fin and the engine cylinder which results in the formation of a skin, as each fin might be aifixed by a bond of the type described above without contacting with the adjacent fins. Moreover the contact between each fin and the engine cylinder may be and referably is continuous it may also be a series of short contacts. It will be noticed that the flow of heat takes place very readily from the inside of the cylinder shell to the fins; a relatively thin iron shell is'preferably used, and the heat passes rapidly to the bond and passes relatively unimpeded over the zones 146, 147 and 148 into the copper 149 of the fins which are usually subjected to cooling air as hereinbefore described. -The melting point of the brazing metal being higher than that attained in the normal operation of the engine, there will be no tendency for the fins to come off the cylinder in the operation of the engine due to the heat of engine opera.- tion, and tests extending over a considerable I eriod indicatethat no deterioratin" action P g tending to weaken the bond takes place after rapid running of the en 'ne for a considerable length of time, so t at the attachment of the fins to the cylinder may be termed a permanent one. It will be found that the union between the fins and the engine cylinder is continuous not only circumferentially between adjacent fins, but also lon itudinally between the shell and the n. The mechanical strength of this union is such that if it is attempted to pull the fins off the cylinder of the dimensions heretofore described, they will break at a point in the copper and not at the point of junction.

It will further be noticed that a large number of copper fins are employed, and that these fins are made of relatively thin copper; each fin is permanently attached to the cast iron cylinder by the intermediary of a heat conducting union which covers an extensive area of the cylinder compared with the cross sectional area of the fin.

Good results have been obtained by the use of a fin in which the height of the fin is in the neighborhood of about times the thickness of the metal of the fin; the total.

number of fins employed and their height and length and distance apart are also preferably predetermined with the view to providing a very extensive heat dissipating surface. This extensive radiating surface is obtained by employing a large number of thin copper fins separated by relatively small air spaces. I

While the union of metals in accordance with the invention may be employed with any thickness of copper fins, I prefer nevertheless to use it with a thin fin such as described herein, and having the advantages referred to.

It will be noted by examination of the strip of finning illustrated in Figs. 7 and 9 that the fins are equidistantly separated and are folded so as to have the inner edges provided with a flat base produced by flaring the inner portions of the several folds or crimps as clearly shown. This form of fin, which may be termend a flare edge or base-formed fin, has been found to have decided advantages. It assists in uniformly spacing the fins apart, and it provides for more equal distribution of the air between the fins.

The preferred form of fin or cooling element consists of a fold or fin loop of sheet metal forming a flattened tube having one edge attached to the cylinder wall. This tube is open at both ends and allows the passage therethrough of a draft of air, while an additional draft of air is caused to pass along the outside of the several fins by surrounding the entire fin structure with a draft Owing to the fact that as described in the grocess of the aforesaid ap lication, Serial- 0. 514,014, the complete nin structure is united with a cylinder in a single bond operation, it follows that each fin is attached to the cylinder by substantially the same amount and thickness of bond metals and the same kind of bond made under exactly the same conditions as its neighbors in other words, the fins are uniformly attached to the cylinder, and this makes uniformity of the flow of heat into the fin in the running of the engine. The bond between the fin structure and the cylinder is substantially the same irrespective of whether the finning is eccentric or concentric; in the case of the eccentric finning shown in Figs. 1 to 6 the finning is shortened at the points where the cylinders of a pair are arranged in proximity with one another. By arranging the cylinders in pairs with the inlet ports of the cylinders adjacent to one another, it becomes possible to reduce the height of the fins between each cylinder of a pair, as said cylinders are cooled on the inlet sides thereof by the incoming fuel mixture. In referring hereinafter to the dimensions of the fins in connection with the concentric finning I shall refer to the height H of the fins as indicating the normal height, such as the height of the majority of fins and not the height of those fins which have been shortened to per-.

mit the engine cylinders to be positioned close together or to permit the passage of valve rods 228.

Special dimensional factors.

It is among the objects of the invention to provide an air cooled internal combustion engine which will run at a very high efficiency, and when used in an automobile vehicle, will give a high mileage per gallon of gasoline or other fuel employed. It is well known that the greater the compression of the engine (within practical limits) the greater the efficiency of the engine from the standpoint range from about sixty-five pounds to the square inch to as high as ninety pounds to the square inch for automobiles; engine compression pressures of sixty-five pounds are referred to as low compression pressures, and a compression pressure of ninety pounds would be referred to as a very high compression pressure for vehicle engines, although compression pressures considerably higher have been employed in airplane engines, said pressures for airplane engines gomg as hlgh as 125 pounds to the square inch. But it must be remembered that such engines must employ a special grade of. fuel, such as a high grade gasoline which is' not generally commercially obtainable all over the country. It is common in water cooled engines to utilize an engine compression of about pounds to a square inch or under, although .in a minority of cases a higher compression pressure is employed in the cylinders.

I have so constructed the present air cooled engine that it can operate with compression pressures at least as high as 75 pounds to the square inch, and at compression pressures which are considerably higher than this average compression pressure of 75 pounds of commercial water' cooled engines emplo ed in automobiles at the present time or operation upon ordinary commercial feuls.

Air cooled engines at present in commercial use for automobiles have generally operated at relativel low compression pressures and considera ly below 75 pounds to the square inch; anyattempt to exceed said compression pressure would be accompanied by extremely objectionable knocking and overheating in the running of the automobile.

The cooling system of my improved internal combustion engine is designed to so reduce the cylinder temperatures that the compression pressure can be carried considerably higher than has heretofore been.

obtained in air cooled engines without extremely objectionable knocking, thereby resulting in'a far more efficient air cooled engine than has heretofore existed. An automobile which is impelled by my new air cooled engine can therefore take hills at full load with little objectionable knocking, notwithstanding its high compression pressure, and in additionsuch an automobile has the advantage of running at a high mileage per gallon of gasoline as compared with an automobile driven by the usual low compression air cooled engine.

The extent to which the temperature of the cylinder can be lowered and the compression increased generally depends upon the following main factors; the number and dimensions of the copper fins; the amount of air passing over the fins; also the relation of the number and dimensions of the fins to the amount of the air passing over them. The number of fins is generally limited by the peripheral area of the cylinder and the thickness of the copper employed; and the dimensions of the fins are governed in part by the conductivity of the copper and other factors hereinafter described. The amount of air flowing over the fins is limited by the power required to drive the fan, inasmuch as therecomes a time when so much power is required to drive the fan to get increased,

cooling that the useful power developed by the engine is diminished owing to the power absorbed by the fan.

I find it desirable to provide as ,many fins as possible per linear inch of the periphery of the cylinder; I have found that excellent results are obtained when there are from 10 to 13 fins er linear inch of the periphery'of the cylin er. I also find that very good results are obtained with a fin the height of which is about 1% inches, although practical considerations may prevent the employment of a fin of such height in automobile engines. Good results have actually been obtained with fins having a height of between 1 to 1 4 inches, although of course I do not in any way limit myself to these dimensions, as they could be considerably less or more, as my invention is not in any way limited to any particular dimension of The thickness of the metal employed in the fins may be determined by a number of considerations, but I find it desirable to maintain a substantially definite ratio between the height and thickness of the fin. I refer this ratio to be in the neighborhood of between 45 to 80; that is the height H of the fin will be between 45 to 80 times the thickness T.

The length of the fin is preferably determined by the distance between the fins. If the fin length is too great relative to the distance between the fins, the air passing between the fins may become saturated with heat before it has completely passed over the entire length of the fins. I find that good results are obtained b my improved fins when the length of the us are made as long as possible, the length being limited by the length of the cylinder, but I prefer that this length should not be greater than between the neighborhood of 60. to 80 times the distance between the fins, a practical length being apparently about times the distance between the fins.

The amount of air flowing over the fins is limited by the power that can be efficiently employed for driving the fan, for while it is true that'the greater the flow of the air stream, the lower the temperature will be, and the greater the compression of the en ine can be made, there comes a time when t e power employed to lower the temperature in this manner is greater than the power gained as a result. 1

I prefer to predetermine the air propolling means or fan with relation to the cooling fins so that the air pro elling means or fan absorbs only a relative y small horse power from .the en 'ne for its operation; in other words my improved structure and dimensions as hereinabove described enable the engine to run at relatively high compression with the utilization of a fan which absorbs onl a small amount of power of the en ine. 11 actual practice I prefer to use a an the horse power of whic is equal to about from 1 to 3 per cent of the total brake horse power of the en ine.

I have secured exce lent results with a 6-cylin-der engine substantially as illustrated herein having finning with the following dimensmnsz- Bore of cylinder 2 1% inches;

Stroke of cylinder 4% inches;

Number of copper fins 116;

Height of fins 1 inches;

Length of fins 6 inches;

Thickness of fins .015 inches;

Compression pressure in engine cylinder, about pounds; and spacing between the fins about 12 or 13 to the inch.

The fan employed, which is of the construction illustrated in the drawing, absorbs about 1 per cent of the brake horse power of the engine.

I prefer to use a very large number of copper fins, and usually about 12 to 13 to the inch. For ordinary commercial uses, there will generally be over fins to a cylinder; for instance in a small cylinder having a bore of 2 A; inches and a stroke of 3 inches, I have actually used 104 fins with good results; in a 4-cylinder engine having a bore of 3 inches and a stroke of 3 inches, I have used 116 fins with good results, In a large bore engine suitable for tractor purposes with a bore of 4% inches and a stroke of 4% inches, I have actually used 17 5 fins.

,It. will be noted that the fan is driven from the engine by a driving connection which permits it to be driven faster than engine speed; therefore the capacity of'the fan is not limited by the s eed of the engine. This makes the capacity 0 the fan independent of the engine speed to the extent that the fan can be driven at the correct speed for the allotment of power for the fan; in other words, as compared with the case where the fan is in the engine flywheel (as is common practice) and must necessarily rotate at the same speed as the engine, I am enabled to make the fan work more nearly in proper relation to the cooling system as a whole, than in the case where the fan is in the flywheel.

While I have described herein a satisfactor form of internal-combustion engine which embodies my invention and have presented preferred dimensions which I have found to give good results, I wish it to be clearlyunderstood that the description of the preferred embodiment and said dimensions herein are given by way of example only, as I believe that the internal-combusmeans that I am the first to provide an-internaL which is permanent, ives excellent thermal contact, is mechanica lystrong, and does not deteriorate substantially under running temperatures and running conditions of an internal-combustion engine. the cylinder asses through the union from the iron to t e copper without substantial obstruction, and the 'fin, being made of copper (which is almost nine times as good a conductor as iron), permits of ready passage of the heat from the cylinder through the copper. This heat'is withdrawn from the copper fins by the cooling air stream, and, owin to the large number of copper fins and their relatively large copper dimensions, the engine has a verylarge heat dissipating surface which increases its cooling efliciency to a marked degree as comared to iron or steel fins common in this art. he engine may, if desired, operate at far higher compressions than have been common with air-cooled engines heretofore, and a marked economy, of operation results from the invention.

While the invention has been described herein more particularly with reference to fins and a finning structure made tocooperate, it will be apparent that the invention in certain of its aspects is not limited to copper but applies to any'other suitable high conductive metal from which the fins may ap ropriately be made.

, 1le the apparatus herein shown and de- The heat fromvrounding'said fins and providing,

scribed constitutes the. preferred embodiment of the invention, it is to be understood *that other forms may be adopted and. 40

changes made, all coming within the scope of the claims which follow, What I claim is as follows: a 1. An engine comprising a cylinder of ferrous metal, a pluralit from a sheet of metal fo ded to provide a series of loops and base portions connecting said loops, the base portions constituting substantlally a continuous sheet around the cylinder and being secured to the cylinder 50 over their entire inner surface by permanent metallic union, a jacket surroundingsaid fins and roviding channels between said loops, and means for causin air to flow through said loops and channe s.

2. The combination with an engine cylinder composed of a metal of low heat conductivit of a series of fins of metal of hi her eat conductivity extendin longitu inally of said cylinder, the'meta of said fins providing a substantially continuous jacket around said cylinder, a casing surin cooperation. with said fins and sai jacket, a series of closed channels, and means for supplying a cooling medium to said channels.

3. tructure as set forth in claim 2, the

said fins and jacket being integral and secured to said cylinder by a union which ermits substantially unobstructed flow of eat 7 from the cylinder to the jacket and fins..

In testimony whereof I h'ereto aflix my signature. 7 CHARLES F. KETTERING.

offins formed 

